SUMMARYPopulations of the saxicolous lichenXanthoparmelia conspersawere sampled from two Potomac River islands. Plummers Island is located below the Cabin John Bridge between Maryland and Virginia, and is subjected to atmospheric fallout from automobile exhaust and road de-icing chemicals. Bear Island is located 6 km upstream of the bridge. Emission- spectrophotometric analysis of lichen material from the two islands revealed a significant accumulation of a number of elements, notably Ca and Pb. Energy-dispersive X-ray microanalysis of the lichen material revealed an observable peak for Ca in the Plummers Island sample. Analysis of three common lichen herbivores, a collembolan (Hypogastrura packardi), and two oribatid mites (Oribata quadripilisandEremaeussp. nearpolitus), revealed a distinct calcium peak in the orbatids sampled from Plummers Island. The collembolan exhibited no detectable calcium accumulation. The recognized importance of lichens as elemental accumulators in terrestrial ecosystems is further defined in terms of nutrient transfers to important soil microarthropods. This mode of element transfer from lichens has not been evaluated adequately.